Excerpts from Books and Wikipedia
"In 1118, a church council at Toulouse decreed that the capture of Zaragoza the northernmost kingdom in the Almoravid realm, could be considered a crusade. . . . one French account says that the pope himself promised forgiveness of sins to those willing to besiege the city. Alfonso had been trying to capture Zaragoza for at least four years. The additional energy provided by the council finally tipped the balance. Noblemen from the south of Western Francia brought their private armies to help out, and the realm fell to the Christian armies in the fall of 1118." [Bauer; Medieval World, p. 664]